Volunteers (N = 31) in the 2002 Houston marathon were assigned to one of two groups: typical hydration (N = 16) and typical hydration supplemented with sodium (N = 15). Sodium supplementation was a 3.4 gm packet of Gatorlytes dissolved in 590 cc of Gatorade and was given at the start, 7, 13, and 20 miles into the race. The number of cups of fluid taken in the race was also tracked.

The sodium-supplemented group was similar to the normal group in post-race sodium, change in sodium weight, finish time, and total amount of fluid taken in the race. Nine Ss spread evenly across the two groups became hyponatremic. Ss who had excessive fluid intake gained weight, ingested more fluid, had lower post-race sodium, and poorer performance times. This condition occurred more in women (6/9 Ss).